Certain illnesses are made manifest by changes in the morphology of some internal structure in the body. These structures, and many others, can be viewed using any of a variety of radiological techniques.
The images that result from any of those radiological techniques are snapshots frozen in time. To identify a change in the morphology, one visually inspects two or more images of the same region of the body. While this procedure is suitable for identifying gross changes in morphology, it is easy to miss more subtle changes.
For example, FIG. 1 shows three successive MRI images representing longitudinal cross-sections of a brain taken some months apart. A close inspection of these images reveals numerous changes in brain morphology. However, these changes are subtle and easily overlooked, even by those trained in the appropriate specialty.